In recent years, various coupling devices have been provided for coupling two fluid storage and/or fluid transport means. Conventional coupling devices are made of two couplings, also called halves, i.e. one plug and one socket. These couplings seal the end of the storage and/transport means, e.g. a hose, to which they are attached in order to prevent leakage. In absence of leakage, the fluid contained in the storage and/or transport means applies a pressure on the couplings. This pressure, also called residual pressure, renders connection of the two couplings very difficult when connection consists in applying a force against said pressure, i.e. pushing a valve in the rear direction of the coupling.
In order to solve these problems, coupling devices have been provided with butterfly valves which can be opened without applying a force against the residual pressure. However these valves require a complicated mechanism involving both rotational and straight movements. Piston-like valve are preferred from that point of view as they have a relatively simple mechanism, i.e. one or more valves biased against the coupling body by one or more springs in order to prevent leakage. However, as mentioned above, opening of these types of valve requires application of a considerable force against the spring and against the residual pressure.
Published European patent application No. 0 265 569 describes a coupling device comprising a pressure relief system in the socket. Said socket comprises a socket body housing a first valve 14 comprising a cylindrical bore and a second valve 22 located and adapted to slide inside said cylindrical bore. The socket comprises two chambers, a first chamber, called space 31, comprising the residual pressure of the fluid and a second unsealed chamber 28 at the front end of the socket. Upon connection of the plug and the socket, the plug first moves the second valve 22 such that a fluid connection is provided between the two chambers and that the residual pressure is evacuated from the first chamber to the second chamber. This device however presents several drawbacks, i.e., the second valve is subjected to the residual pressure because of a hole 29 provided in the first valve. Therefore, a large amount of effort is needed to move said first valve before pressure evacuation. Also, the second chamber is not sealed and can therefore be subject to any type of contamination. Finally, as the front end and the second chamber are not sealed, the socket can therefore be coupled only with specific plugs which provide sealing at the moment of decompression, i.e. the moment where fluid communication is realized between the two chambers, otherwise leakage may occur.
U.S. Pat. No. 5,996,624 describes a quick-coupling device comprising a pressure relief system made of three different valves. A first valve 31, a second valve 40 and a third valve 50 are positioned along the longitudinal direction of the plug body such that upon connection, a piston of the socket pushes the first valve which in turn pushes the second valve that finally pushes the third valve thus providing fluid connection between a rear chamber and a front chamber of the socket. However, in this device the third valve is subjected to the residual pressure and its displacement therefore requires a large amount of effort.